The present invention relates to a method for realizing a device detecting inner pressure lowering of tires at low cost and precisely.
Methods of detecting inner pressure lowering of tires from vehicle speed and distance which are calculated from GPS (Global Positioning System) information and rotational speed of tires have been conventionally disclosed in JP-A-2005-186739, JP-A-2003-146037, JP-A-2003-94920 and the like. However, it is necessary to detect change in rotational speed of tires only by inner pressure lowering in order to detect the inner pressure lowering of tires from vehicle speed which is calculated from GPS information and rotational speed of tires. Namely, it is necessary to exclude rotational speed change depending on a running state of a vehicle.
JP-A-2003-94920 discloses a method by which inner pressure lowering of tires is detected by comparing the running locus of a vehicle calculated from rotational information of tires with the running locus of a vehicle obtained from vehicle positional information by GPS and the like, but the exclusion of the rotational speed change depending on a running state of a vehicle is not indicated. Further, JP-A-2005-186739 and JP-A-2003-146037 specify a running state from comparison of the rotational state of mutual tires, but when inner pressure lowering of tires is generated, the relation of the rotational speed of mutual four wheels has already been unbalanced, therefore an accurate running state cannot be specified.
Further, there is also known a method of detecting inner pressure lowering of tires by calculating dynamic load radii of tires from a moving distance calculated from GPS information and rotational speed of tires, but since exclusion of rotational speed change depending on the running state of a vehicle is inadequate, precision is also inadequate.
Consequently, there is devised a method of detecting inner pressure lowering of tires by calculating a running speed of a vehicle utilizing satellite electric wave utilized for GPS and by calculating the dynamic load radii of tires from the speed information and rotational angular speed information of tires (see JP-A-2005-230791). However, the method had problems that when GPS signals cannot be received (in a building shade, woody zone and the like), dynamic load radii cannot be calculated and inner pressure lowering of tires cannot be detected.